Device including transparent layer with profiled surface for improved extraction

ABSTRACT

A profiled surface for improving the propagation of radiation through an interface is provided. The profiled surface includes a set of large roughness components providing a first variation of the profiled surface having a characteristic scale approximately an order of magnitude larger than a target wavelength of the radiation. The set of large roughness components can include a series of truncated shapes. The profiled surface also includes a set of small roughness components superimposed on the set of large roughness components and providing a second variation of the profiled surface having a characteristic scale on the order of the target wavelength of the radiation.

REFERENCE TO RELATED APPLICATIONS

The current application is a continuation of U.S. application Ser. No.14/297,656, which was filed on 6 Jun. 2014, and which iscontinuation-in-part of U.S. application Ser. No. 13/517,711, which wasfiled on 14 Jun. 2012, and which claims the benefit of U.S. ProvisionalApplication No. 61/497,489, which was filed on 15 Jun. 2011, all ofwhich are hereby incorporated by reference.

GOVERNMENT LICENSE RIGHTS

This invention was made with Federal government support under ContractNo. W911 NF-10-2-0023 awarded by Defense Advanced Research ProjectsAgency (DARPA). The government has certain rights in the invention.

TECHNICAL FIELD

The disclosure relates generally to emitting devices, and moreparticularly, to an emitting device with improved light extraction.

BACKGROUND ART

Semiconductor emitting devices, such as light emitting diodes (LEDs) andlaser diodes (LDs), include solid state emitting devices composed ofgroup III-V semiconductors. A subset of group III-V semiconductorsincludes group III nitride alloys, which can include binary, ternary andquaternary alloys of indium (In), aluminum (Al), gallium (Ga), andnitrogen (N). Illustrative group III nitride based LEDs and LDs can beof the form In_(y)Al_(x)Ga_(1-x-y)N, where x and y indicate the molarfraction of a given element, 0≦x, y≦1, and 0≦x+y≦1. Other illustrativegroup III nitride based LEDs and LDs are based on boron (B) nitride (BN)and can be of the form Ga_(z)In_(y)Al_(x)B_(1-x-y-z)N, where 0≦x, y,z≦1, and 0≦x+y+z≦1.

An LED is typically composed of semiconducting layers. During operationof the LED, an applied bias across doped layers leads to injection ofelectrons and holes into an active layer where electron-holerecombination leads to light generation. Light is generated with uniformangular distribution and escapes the LED die by traversing semiconductorlayers in all directions. Each semiconducting layer has a particularcombination of molar fractions (e.g., x, y, and z) for the variouselements, which influences the optical properties of the layer. Inparticular, the refractive index and absorption characteristics of alayer are sensitive to the molar fractions of the semiconductor alloy.

An interface between two layers is defined as a semiconductorheterojunction. At an interface, the combination of molar fractions isassumed to change by a discrete amount. A layer in which the combinationof molar fractions changes continuously is said to be graded. Changes inmolar fractions of semiconductor alloys can allow for band gap control,but can lead to abrupt changes in the optical properties of thematerials and result in light trapping. A larger change in the index ofrefraction between the layers, and between the substrate and itssurroundings, results in a smaller total internal reflection (TIR) angle(provided that light travels from a high refractive index material to amaterial with a lower refractive index). A small TIR angle results in alarge fraction of light rays reflecting from the interface boundaries,thereby leading to light trapping and subsequent absorption by layers orLED metal contacts.

Roughness at an interface allows for partial alleviation of the lighttrapping by providing additional surfaces through which light can escapewithout totally internally reflecting from the interface. Nevertheless,light only can be partially transmitted through the interface, even ifit does not undergo TIR, due to Fresnel losses. Fresnel losses areassociated with light partially reflected at the interface for all theincident light angles. Optical properties of the materials on each sideof the interface determines the magnitude of Fresnel losses, which canbe a significant fraction of the transmitted light.

SUMMARY OF THE INVENTION

Aspects of the invention provide a profiled surface for improving thepropagation of radiation through an interface. The profiled surfaceincludes a set of large roughness components providing a first variationof the profiled surface having a characteristic scale approximately anorder of magnitude larger than a target wavelength of the radiation. Theset of large roughness components can include a series of truncatedshapes. The profiled surface also includes a set of small roughnesscomponents superimposed on the set of large roughness components andproviding a second variation of the profiled surface having acharacteristic scale on the order of the target wavelength of theradiation.

A first aspect of the invention provides a device comprising: an atleast partially transparent layer having a first side and a second side,wherein radiation enters the at least partially transparent layerthrough the first side and exits the at least partially transparentlayer through the second side, and wherein at least one of the firstside or the second side comprises a profiled surface, the profiledsurface including: a set of large roughness components providing a firstvariation of the profiled surface having a characteristic scaleapproximately an order of magnitude larger than a target wavelength ofthe radiation, wherein the set of large roughness components comprise aseries of truncated shapes; and a set of small roughness componentsproviding a second variation of the profiled surface having acharacteristic scale on the order of the target wavelength of theradiation, wherein the set of small roughness components aresuperimposed on the set of large roughness components.

A second aspect of the invention provides a method comprising: designinga profiled surface for an at least partially transparent layer of adevice, wherein radiation passes through the profiled surface duringoperation of the device, wherein the profiled surface includes: a set oflarge roughness components providing a first non-uniform variation ofthe profiled surface having a characteristic scale approximately anorder of magnitude larger than a target wavelength of the radiation,wherein the set of large roughness components comprise a series oftruncated shapes; and a set of small roughness components providing asecond non-uniform variation of the profiled surface having acharacteristic scale on the order of the target wavelength of theradiation, wherein the set of small roughness components aresuperimposed on the set of large roughness components.

A third aspect of the invention provides an emitting device comprising:an active region configured to generate radiation having a peakwavelength; and an at least partially transparent layer on a first sideof the active region, wherein radiation generated in the active regionpasses through the at least partially transparent layer, and wherein theat least partially transparent layer includes at least one profiledsurface, wherein the at least one profiled surface includes: a set oflarge roughness components providing a first variation of the profiledsurface having a characteristic scale approximately an order ofmagnitude larger than a target wavelength of the radiation, wherein theset of large roughness components comprise a series of truncated shapes;and a set of small roughness components providing a second variation ofthe profiled surface having a characteristic scale on the order of thetarget wavelength of the radiation, wherein the set of small roughnesscomponents are superimposed on the set of large roughness components.

The illustrative aspects of the invention are designed to solve one ormore of the problems herein described and/or one or more other problemsnot discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the disclosure will be more readilyunderstood from the following detailed description of the variousaspects of the invention taken in conjunction with the accompanyingdrawings that depict various aspects of the invention.

FIG. 1 shows a schematic structure of an illustrative emitting deviceaccording to an embodiment.

FIGS. 2A and 2B show an illustrative roughness element and anillustrative model for a roughness element, respectively, according toan embodiment.

FIG. 3 shows the effect of the small roughness component on transmissionover a range of angles of incidence according to an embodiment.

FIG. 4 shows the effect of the dimensions of the small roughnesscomponent on the graded refractive index according to an embodiment.

FIGS. 5A and 5B show illustrative schematics of roughness elements witha constant index of refraction and a graded index of refraction,respectively, according to an embodiment.

FIGS. 6A and 6B show illustrative distributions of light and thecorresponding light extraction efficiencies (LEE) for a constant indexof refraction cone and a graded index of refraction cone, respectively,according to an embodiment.

FIGS. 7A-7C show illustrative large roughness components and acorresponding illustrative polar plot of intensity according toembodiments.

FIGS. 8A-8B show illustrative profiled surfaces according toembodiments.

FIGS. 9A-9B show illustrative profiled surfaces according toembodiments.

FIG. 10 shows an illustrative flow diagram for fabricating a circuitaccording to an embodiment.

It is noted that the drawings may not be to scale. The drawings areintended to depict only typical aspects of the invention, and thereforeshould not be considered as limiting the scope of the invention. In thedrawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION OF THE INVENTION

As indicated above, aspects of the invention provide a profiled surfacefor improving the propagation of radiation through an interface. Theprofiled surface includes a set of large roughness components providinga first variation of the profiled surface having a characteristic scaleapproximately an order of magnitude larger than a target wavelength ofthe radiation. The set of large roughness components can include aseries of truncated shapes. The profiled surface also includes a set ofsmall roughness components superimposed on the set of large roughnesscomponents and providing a second variation of the profiled surfacehaving a characteristic scale on the order of the target wavelength ofthe radiation. As used herein, unless otherwise noted, the term “set”means one or more (i.e., at least one) and the phrase “any solution”means any now known or later developed solution.

Turning to the drawings, FIG. 1 shows a schematic structure of anillustrative emitting device 10 according to an embodiment. In a moreparticular embodiment, the emitting device 10 is configured to operateas a light emitting diode (LED), such as a conventional or superluminescent LED. Alternatively, the emitting device 10 can be configuredto operate as a laser diode (LD). In either case, during operation ofthe emitting device 10, application of a bias comparable to the band gapresults in the emission of electromagnetic radiation from an activeregion 18 of the emitting device 10. The electromagnetic radiationemitted by the emitting device 10 can comprise a peak wavelength withinany range of wavelengths, including visible light, ultravioletradiation, deep ultraviolet radiation, infrared light, and/or the like.

The emitting device 10 includes a heterostructure comprising a substrate12, a buffer layer 14 adjacent to the substrate 12, an n-type claddinglayer 16 (e.g., an electron supply layer) adjacent to the buffer layer14, and an active region 18 having an n-type side 19A adjacent to then-type cladding layer 16. Furthermore, the heterostructure of theemitting device 10 includes a p-type layer 20 (e.g., an electronblocking layer) adjacent to a p-type side 19B of the active region 18and a p-type cladding layer 22 (e.g., a hole supply layer) adjacent tothe p-type layer 20.

In a more particular illustrative embodiment, the emitting device 10 isa group III-V materials based device, in which some or all of thevarious layers are formed of elements selected from the group III-Vmaterials system. In a still more particular illustrative embodiment,the various layers of the emitting device 10 are formed of group IIInitride based materials. Group III nitride materials comprise one ormore group III elements (e.g., boron (B), aluminum (Al), gallium (Ga),and indium (In)) and nitrogen (N), such that B_(W)Al_(X)Ga_(Y)IN_(Z)N,where 0≦W, X, Y, Z≦1, and W+X+Y+Z=1. Illustrative group III nitridematerials include AlN, GaN, InN, BN, AlGaN, AlInN, AlBN, AlGaInN,AlGaBN, AlInBN, and AlGaInBN with any molar fraction of group IIIelements.

An illustrative embodiment of a group III nitride based emitting device10 includes an active region 18 (e.g., a series of alternating quantumwells and barriers) composed of In_(y)Al_(x)Ga_(1-x-y)N,Ga_(z)In_(y)Al_(x)B_(1-x-y-z)N, an Al_(x)Ga_(1-x)N semiconductor alloy,or the like. Similarly, both the n-type cladding layer 16 and the p-typelayer 20 can be composed of an In_(y)Al_(x)Ga_(1-x-y)N alloy, aGa_(z)In_(y)Al_(x)B_(1-x-y-z)N alloy, or the like. The molar fractionsgiven by x, y, and z can vary between the various layers 16, 18, and 20.The substrate 12 can be sapphire, silicon carbide (SiC), silicon (Si),GaN, AlGaN, AlON, LiGaO₂, or another suitable material, and the bufferlayer 14 can be composed of AlN, an AlGaN/AlN superlattice, and/or thelike.

As shown with respect to the emitting device 10, a p-type metal 24 canbe attached to the p-type cladding layer 22 and a p-type contact 26 canbe attached to the p-type metal 24. Similarly, an n-type metal 28 can beattached to the n-type cladding layer 16 and an n-type contact 30 can beattached to the n-type metal 28. The p-type metal 24 and the n-typemetal 28 can form ohmic contacts to the corresponding layers 22, 16,respectively. In an embodiment, the p-type metal 24 and the n-type metal28 each comprise several conductive and reflective metal layers, whilethe n-type contact 30 and the p-type contact 26 each comprise highlyconductive metal. In an embodiment, the p-type cladding layer 22 and/orthe p-type contact 26 can be at least partially transparent (e.g.,semi-transparent or transparent) to the electromagnetic radiationgenerated by the active region 18. For example, the p-type claddinglayer 22 and/or the p-type contact 26 can comprise a short periodsuperlattice lattice structure, such as an at least partiallytransparent magnesium (Mg)-doped AlGaN/AlGaN short period superlatticestructure (SPSL). Furthermore, the p-type contact 26 and/or the n-typecontact 30 can be at least partially reflective of the electromagneticradiation generated by the active region 18. In another embodiment, then-type cladding layer 16 and/or the n-type contact 30 can be formed of ashort period superlattice, such as an AlGaN SPSL, which is at leastpartially transparent to the electromagnetic radiation generated by theactive region 18.

As used herein, a layer is at least partially transparent when the layerallows at least a portion of electromagnetic radiation in acorresponding range of radiation wavelengths to pass there through. Forexample, a layer can be configured to be at least partially transparentto a range of radiation wavelengths corresponding to a peak emissionwavelength for the light (such as ultraviolet light or deep ultravioletlight) emitted by the active region 18 (e.g., peak emission wavelength+/− five nanometers). As used herein, a layer is at least partiallytransparent to radiation if it allows more than approximately 0.5percent of the radiation to pass there through. In a more particularembodiment, an at least partially transparent layer is configured toallow more than approximately five percent of the radiation to passthere through. Similarly, a layer is at least partially reflective whenthe layer reflects at least a portion of the relevant electromagneticradiation (e.g., light having wavelengths close to the peak emission ofthe active region). In an embodiment, an at least partially reflectivelayer is configured to reflect at least approximately five percent ofthe radiation.

As further shown with respect to the emitting device 10, the device 10can be mounted to a submount 36 via the contacts 26, 30. In this case,the substrate 12 is located on the top of the emitting device 10. Tothis extent, the p-type contact 26 and the n-type contact 30 can both beattached to a submount 36 via contact pads 32, 34, respectively. Thesubmount 36 can be formed of aluminum nitride (AlN), silicon carbide(SiC), and/or the like.

Any of the various layers of the emitting device 10 can comprise asubstantially uniform composition or a graded composition. For example,a layer can comprise a graded composition at a heterointerface withanother layer. In an embodiment, the p-type layer 20 comprises a p-typeblocking layer having a graded composition. The graded composition(s)can be included to, for example, reduce stress, improve carrierinjection, and/or the like. Similarly, a layer can comprise asuperlattice including a plurality of periods, which can be configuredto reduce stress, and/or the like. In this case, the composition and/orwidth of each period can vary periodically or aperiodically from periodto period.

It is understood that the layer configuration of the emitting device 10described herein is only illustrative. To this extent, an emittingdevice/heterostructure can include an alternative layer configuration,one or more additional layers, and/or the like. As a result, while thevarious layers are shown immediately adjacent to one another (e.g.,contacting one another), it is understood that one or more intermediatelayers can be present in an emitting device/heterostructure. Forexample, an illustrative emitting device/heterostructure can include anundoped layer between the active region 18 and one or both of the p-typecladding layer 22 and the electron supply layer 16.

Furthermore, an emitting device/heterostructure can include aDistributive Bragg Reflector (DBR) structure, which can be configured toreflect light of particular wavelength(s), such as those emitted by theactive region 18, thereby enhancing the output power of thedevice/heterostructure. For example, the DBR structure can be locatedbetween the p-type cladding layer 22 and the active region 18.Similarly, a device/heterostructure can include a p-type layer locatedbetween the p-type cladding layer 22 and the active region 18. The DBRstructure and/or the p-type layer can comprise any composition based ona desired wavelength of the light generated by thedevice/heterostructure. In one embodiment, the DBR structure comprises aMg, Mn, Be, or Mg+Si-doped p-type composition. The p-type layer cancomprise a p-type AlGaN, AlInGaN, and/or the like. It is understood thata device/heterostructure can include both the DBR structure and thep-type layer (which can be located between the DBR structure and thep-type cladding layer 22) or can include only one of the DBR structureor the p-type layer. In an embodiment, the p-type layer can be includedin the device/heterostructure in place of an electron blocking layer. Inanother embodiment, the p-type layer can be included between the p-typecladding layer 22 and the electron blocking layer.

Regardless, as illustrated in FIG. 1, the device 10 can include one ormore at least partially reflective layers on a first side of the activeregion 18 and one or more layers having a profiled surface 40A-40C on anopposing side of the active region 18 through which radiation generatedin the active region 18 can leave the device 10. As illustrated, eachprofiled surface 40A-40C is configured to provide a boundary for aninterface between two adjacent layers and/or an interface between thedevice 10 and the surrounding environment that is uneven or rough ratherthan substantially smooth. In an embodiment, the device 10 can include aprofiled surface 40A-40C at each interface where the refractive indexchanges abruptly (e.g., a difference in refractive indexes greater thanor equal to approximately five percent). For example, as describedherein, the substrate 12 can be made of sapphire, the buffer layer 14can be AlN, and the cladding layer 14 can be AlGaN. For an illustrativetarget wavelength, these materials can have indexes of refraction of1.8, 2.3, and 2.5, respectively. To this extent, the device 10 is shownincluding a profiled surface 40A at the interface between the substrate12 and the environment (which has an index of refraction ofapproximately one); a profiled surface 40B at the interface between thebuffer layer 14 and the substrate 12; and/or a profiled surface 40C atthe interface between the n-type cladding layer 16 and the buffer layer14. In this case, the buffer layer 14 can act as a light extraction filminserted between two materials with two different refraction indexes toprovide a more gradual transition of refraction indexes.

It is understood that various embodiments of the device 10 can include aprofiled surface configured as described herein at any combination ofone or more interfaces. To this extent, a profiled surface can beincluded on any type of group III-nitride based semiconductor surface,such as AlInGaN or AlBGaN semiconductor alloys. Furthermore, a profiledsurface can be included, for example, on an ultraviolet transparentglass, a polymer with a matched index deposited over a group III-nitridebased semiconductor surface, and/or the like.

Each profiled surface 40A-40C can be configured to improve theextraction of radiation from a corresponding at least partiallytransparent layer 12, 14, 16, respectively. For example, duringoperation of the device 10, radiation can be generated in the activeregion 18 and travel through at least partially transparent layers 16,14, 12, before being emitted from the device 10. The profiled surfaces40C, 40B can be configured to increase the amount of radiation thatexits a first layer 16, 14 and enters an adjacent layer 14, 12,respectively, as compared to a device having substantially smoothboundaries between the layers 12, 14, 16. Similarly, the profiledsurface 40A can be configured to increase the amount of radiation thatexits the device 10, e.g., via substrate 12, and enters into thesurrounding environment, as compared to a device having a substantiallysmooth outer surface.

As illustrated, a profiled surface 40A-40C can be formed using aplurality of roughness elements, such as roughness elements 42A, 42Bforming a part of the profiled surface 40A. Each roughness element 42A,42B can be configured to provide additional surfaces for reflecting andrefracting light, thereby facilitating light extraction from thecorresponding layer (e.g., the substrate 12). In an embodiment, aroughness element 42A, 42B is formed of a large roughness component, onwhich is superimposed a small roughness component as described herein.While each of the profiled surfaces 40A-40C are shown including aparticular number of roughness elements 42A, 42B, each of which isconfigured substantially similar to the other, it is understood thateach profiled surface 40A-40C can be formed of any number of roughnesselements having any combination of configurations.

In an embodiment, the large roughness components of the roughnesselements 42A, 42B provide variation of the profiled surface 40A having acharacteristic scale greater than a target wavelength. The targetwavelength can be selected based on a peak wavelength of the radiationdesired to pass through the interface during operation of the device 10and can be within any range of wavelengths, including visible light,ultraviolet radiation, deep ultraviolet radiation, infrared light,and/or the like. In an embodiment, the target wavelength corresponds tothe peak wavelength of the radiation generated in the active region 18.In a more particular embodiment, the characteristic scale of thevariation provided by the large roughness components is approximately anorder of magnitude (e.g., ten times) larger than the target wavelength,and can be determined based on the average height and/or width of thelarge roughness components. In an embodiment, the large roughnesscomponents have comparable heights and widths, e.g., of approximatelytwo to four micrometers. Inclusion of the large roughness components canreduce losses associated with TIR.

Additionally, the small roughness components of the roughness elements42A, 42B can provide variation of the profiled surface 40A having acharacteristic scale on the order of the target wavelength. To thisextent, the characteristic scale of the variation provided by the smallroughness components can be between approximately ten to two hundredpercent of the target wavelength, and can be determined based on theaverage height of the small roughness components. In an embodiment, thesmall roughness components have heights between approximately ten to onehundred nanometers. Inclusion of the small roughness components canreduce Fresnel losses. Furthermore, the small roughness components canform a photonic crystal, which is configured to guide the radiation of atarget wavelength to facilitate its extraction from the layer.

FIGS. 2A and 2B show an illustrative roughness element 42 and anillustrative roughness element model 50, respectively, according to anembodiment. As illustrated in FIG. 2A, the roughness element 42 includesa large roughness component 44 on which is superimposed a smallroughness component 46. The large roughness component 44 is shown havinga truncated triangular cross section, which can correspond to atruncated cone or a truncated pyramid having any number of sides. Thesmall roughness component 46 is illustrated as a series of peaks andvalleys of material having random variations in heights and locationsextending from the truncated portion 45 of the large roughness component44. The small roughness component 46 can reduce Fresnel losses. Asillustrated in FIG. 2B, the roughness element model 50 can include alarge roughness component model 52 and a small roughness component model54. The large roughness component model 52 can comprise, for example, atruncated cone or a truncated pyramid shape. The small roughnesscomponent model 54 can model the small roughness component 46 as anintermediate layer having a thickness L, where the thickness correspondsto the characteristic scale of the small roughness component 46 and canbe measured as the distance between the lowest valley and the highestpeak on the roughness element 42.

The small roughness component 46 can introduce a graded refractive indexinto the roughness element 42. In particular, for a given height h alongthe thickness L of the intermediate layer of the small roughnesscomponent model 54, a corresponding index of refraction can be estimatedby calculating an average between the refractive index of the materialforming the roughness element 42 and the material adjacent to theroughness element 42 (e.g., the layer/environment into which theradiation is transmitted after exiting the roughness element 42), wherethe average is weighted by a fractional cross sectional area of thesmall roughness component 46 at the given height h.

FIG. 3 shows the effect of the small roughness component 46 (FIG. 2A) ontransmission (T) over a range of angles of incidence (Θ) according to anembodiment. In this case, the roughness element is included at aninterface between a sapphire substrate 12 (FIG. 1) having an index ofrefraction n=1.825 and the surrounding air (having an index ofrefraction approximately equal to 1) for radiation having a givenwavelength in a vacuum, λ₀. As illustrated, when the small roughnesscomponent 46 is not included (i.e., L=0λ₀), the transmission has amaximum of approximately 0.92 and begins to drop significantly when theangle of incidence exceeds approximately twenty degrees. When the smallroughness component 46 has a thickness L of approximately 0.25λ₀, themaximum transmission increases to approximately 0.98 and is maintaineduntil the angle of incidence exceeds approximately twenty-eight degrees.When the small roughness component 46 has a thickness L betweenapproximately 0.5λ₀ to 1λ₀ or greater, the transmission exceeds 0.99until the angle of incidence exceeds approximately twenty-eight degrees.As a result, the small roughness component 46 can reduce the Fresnellosses, which results in higher radiation extraction from the sapphiresubstrate 12 as compared to an interface without the small roughnesscomponent 46.

FIG. 4 shows the effect of the dimensions of the small roughnesscomponent 46 on the graded refractive index according to an embodiment.As illustrated, the graded refractive index gradually transitions fromthe refractive index of the material of the small roughness component 46(e.g., sapphire) to the refractive index of the adjacent material (e.g.,air) as the distance, z, from the large roughness component 44 (FIG. 2A)increases.

FIGS. 5A and 5B show illustrative schematics of roughness elements 60A,60B with a constant index of refraction and a graded index ofrefraction, respectively, according to an embodiment. In each case, alight emitting source is located at a base of the cone in the rightmostsurface of the adjoining cylinder 62. The walls of the cylinder 62 areset to be partially absorbing mirrors to mimic absorption of light in atypical light emitting diode. The roughness element 60A comprises a coneshape with smooth sides. In contrast, the roughness element 60Bcomprises a cone shape (e.g., a large roughness component) with sideshaving small roughness components superimposed thereon. As a result, thesides of the roughness element 60B have a fuzzy look as compared to thesides of the roughness element 60A.

FIGS. 6A and 6B show illustrative distributions of light and thecorresponding light extraction efficiencies (LEE) for the cones 60A, 60Bof FIGS. 5A and 5B, respectively, according to an embodiment. Asillustrated, the LEE (shown in FIG. 6B) for the transmission of lightthrough the cone 60B having a graded index of refraction is clearlyhigher than the LEE (shown in FIG. 6A) for the transmission of lightthrough the cone 60A having a constant index of refraction, e.g., animprovement of over ten percent.

FIGS. 7A-7C show illustrative large roughness components 70A, 70B and acorresponding illustrative polar plot of intensity, respectively,according to embodiments. In FIG. 7A, the large roughness component 70Ais in the shape of a truncated cone, while the large roughness component70B of FIG. 7B is in the shape of a truncated pyramid. Each largeroughness component 70A, 70B can comprise an inverse truncated element,where the base B, which is the portion of the large roughness component70A, 70B adjacent to the corresponding layer (e.g., substrate 12), issmaller than the top T. While not shown, it is understood that eachlarge roughness component 70A, 70B can be used to form a roughnesselement by superimposing a small roughness component on, for example,the top surface of the truncated shape. Furthermore, while the truncatedpyramid of the large roughness component 70B is shown having a base andtop with four sides, it is understood that the base and top of thepyramid can be a polygon with any number of sides.

Such a configuration for the large roughness components 70A, 70B can beused, for example, for light focusing in order to facilitate extractionof light from the layer, e.g., by designing the large roughnesscomponents 70A, 70B to determine an emission cone angle for radiation ofthe target wavelength. To this extent, the sides of the truncated coneshape of the large roughness component 70A can form an angle Θ of lessthan ninety degrees. Similarly, the sides of the truncated pyramid shapeof the large roughness component 70B and the sides of the truncated coneshape of the large roughness component 44A can form an angle withrespect to the normal of less than forty-five degrees. In this manner,an increased amount of light reflections will result in the light beingdirected out from the layer. FIG. 7C shows an illustrative polar plot ofintensity distribution for the large roughness component 70A.

FIGS. 8A-8B show illustrative profiled surfaces 400A, 400B according toembodiments. In each case, it is understood that while only the set oflarge roughness components of each profiled surface 400A, 400B are shownfor clarity, each profiled surface 400A, 400B can include a set of smallroughness components (e.g., the set of small roughness components 46 inFIG. 2A) superimposed on the set of large roughness components asdescribed herein. As illustrated in the figures and described herein,the set of large roughness components can include a series of truncatedshapes.

In FIG. 8A, the profiled surface 400A includes a set of large roughnesscomponents 80A-80E. A first portion of the set of large roughnesscomponents (e.g., components 80A-80D) includes a series of truncatedtriangular cross sections, each of which can correspond to a truncatedcone or a truncated pyramid having any number of sides. A second portionof the set of large roughness components (e.g., component 80E) includesone or more inverse truncated triangular cross sections. For example,the large roughness components 80A-80D each include a base B₁ that islarger than a top T₁. The base B₁ is the portion of the large roughnesscomponent 80A-80D that is adjacent to the corresponding layer (e.g.,substrate 12), and is smaller than the top T₁. Conversely, the inversetruncated large roughness component 80E includes a base B₂ that issmaller than a top T₂. In FIG. 8B, the profiled surface 400B includes afirst portion of the set of large roughness components including one ormore truncated components (e.g., component 82A) and a second portion ofthe set of large roughness components including a series of inversetruncated large roughness components (e.g., components 82B-82E). It isunderstood that the profiled surfaces 400A, 400B can include any numberof truncated large roughness components and any number of inversetruncated large roughness components. In an embodiment, the truncatedlarge roughness components can be at least approximately twenty percentof the large roughness components located on the profiled surface. Inanother embodiment, the inverse truncated large roughness components canbe at least approximately twenty percent of the large roughnesscomponents located on the profiled surface.

FIGS. 9A-9B show illustrative profiled surfaces 402A, 402B according toembodiments. In each case, it is understood that while only the set oflarge roughness components of each profiled surfaces 402A, 402B areshown for clarity, each profiled surface 402A, 402B can include a set ofsmall roughness components (e.g., the set of small roughness components46 in FIG. 2A) superimposed on the set of large roughness components asdescribed herein. As illustrated in the figures and described herein,the set of large roughness components can concurrently include a seriesof truncated shapes and a series of non-truncated shapes. Thisconfiguration can be useful, for example, as a parameter for lightscattering.

In FIG. 9A, the profiled surface 402A includes a set of large roughnesscomponents 90A-90E. A first portion of the set of large roughnesscomponents (e.g., component 90A) includes one or more components havingtruncated triangular cross sections, which can correspond to a truncatedcone or a truncated pyramid having any number of sides. A second portionof the set of large roughness components (e.g., 90B-90E) includescomponents having non-truncated triangular cross sections. In FIG. 9B,the profiled surface 402B includes a first portion of the set of largeroughness components including one or more non-truncated large roughnesscomponents (e.g., component 92A) and a second portion of the set oflarge roughness components including truncated large roughnesscomponents (e.g., components 92B-92E). It is understood that theprofiled surfaces 402A, 402B can include any number of truncated largeroughness components and any number of non-truncated large roughnesscomponents. In an embodiment, for example, the truncated large roughnesscomponents can be at least approximately twenty percent of the largeroughness components located on the profiled surface. In anotherembodiment, for example, the non-truncated large roughness componentscan be at least approximately twenty percent of the large roughnesscomponents located on the profiled surface.

In each case shown in FIGS. 8A-8B and 9A-9B, the first portion of theset of large roughness components (e.g., components 80A-80D in FIG. 8A)can be interspersed with the second portion of the set of largeroughness components (e.g., component 80E in FIG. 8A) on the profiledsurface in any one or two dimensional pattern. Although the firstportion of the set of large roughness components in FIGS. 8A-8B areshown as grouped together, it is understood that the first and thesecond portion of the set of large roughness components can be anywherealong the profiled surface and are not necessarily grouped together. Forexample, in FIG. 8A, component 80E can be placed between component 80Aand component 80B, between component 80B and component 80C; betweencomponent 80C and component 80D, and/or the like. Furthermore, if morethan one component is in both the first portion and the second portionof the set of large roughness components, it is understood that thefirst portion and the second portion can be interspersed in any regular,semi-regular, or random pattern. To this extent, the first portion andthe second portion of the set of large roughness components can form analternating pattern of large roughness components.

In one embodiment, the large roughness components or large truncatedroughness components (herein referred to as large components or largeelements) may be collocated in a different portion of the profiledsurface than a portion of the profiled surface on which the inversetruncated large roughness elements (herein referred to as inversecomponents or elements) are located. Such a configuration can beutilized, e.g., in order to affect the distribution of intensity ofradiation emitted from the corresponding device (e.g., a UV LED). Forexample, the large elements may be collocated in a centrally located(e.g., middle) portion of an exit face of the LED device, occupyingapproximately 20-50% of the surface area of the exit face, and theinverse components can surround the region containing large elements. Itis understood that other collocations of large elements and inverseelements are possible. One approach for designing a collocation patternuses ray tracing simulation and an optimization algorithm to obtain atarget distribution of intensity of radiation emitted from the device.Such a process can be roughly understood as a series of steps, where inorder to obtain or approximate a target intensity distribution overpolar angles, the collocation pattern is adjusted until a local orglobal optimum condition corresponding to the target intensitydistribution is found. It is further understood that in order tooptimize the intensity distribution over polar angles with respect to atarget intensity distribution, as well as an overall efficiency of thedevice, not only collocation of large and inverted components can bevaried, but also the collocation of elements containing small roughnessscale. For example, the large elements positioned in the central portionof the exit face may contain small scale roughness elements, whereas theinverse elements may not contain such small scale roughness elements.

Returning to FIG. 1, it is understood that a device 10, or aheterostructure used in forming a device 10, including one or morelayers having a profiled surface, such as layers 12, 14, and 16, can befabricated using any solution. For example, an emittingdevice/heterostructure can be manufactured by obtaining (e.g., forming,preparing, acquiring, and/or the like) a substrate 12, forming (e.g.,growing, depositing, adhering, and/or the like) a buffer layer 14thereon, and forming an n-type cladding layer 16 over the buffer layer14. Furthermore, the active region 18, e.g., including quantum wells andbarriers, can be formed over the n-type cladding layer 16 using anysolution. The p-type layer 20 can be formed over the active region 18and the p-type cladding layer 22 can be formed on the p-type layer 20using any solution. Additionally, one or more metal layers, contacts,and/or additional layers can be formed using any solution. Furthermore,the heterostructure/device can be attached to a submount via contactpads.

It is understood that the fabrication of the emittingdevice/heterostructure can include the deposition and removal of atemporary layer, such as mask layer, the patterning one or more layers,the formation of one or more additional layers not shown, and/or thelike. To this extent, a profiled surface 40A-40C (or profiled surfaces400A, 400B, 402A, 402B) can be fabricated using any combination ofdeposition and/or etching. For example, the fabrication can includeselective deposition and/or etching of nanoscale objects, such asnanodots and/or nanorods, of the material to form the large and/or smallroughness components. Such deposition and/or etching can be used to formperiodic and/or non-periodic random patterns.

In fabricating the profiled surfaces discussed herein, a simulationusing ray tracing and an optimization algorithm, such as a geneticalgorithm, can be performed. An illustrative embodiment of the processof simulation can comprise:

a) Modeling an optical structure of a light emitting diode (LED), whichcan include incorporating domains with their respective opticalproperties and assigning volumes or surfaces for emission of light;

b) Evaluating an efficiency of the LED and intensity of radiated lightby collecting emitted rays on the surface of a control detecting spheresurrounding the LED;

c) Incorporating a set of roughness elements on a set of LED surfaces asdescribed herein;

d) Establishing a set of optimization parameters for modeling roughness,such as roughness shape, size, location, reflective/transmittalproperties of roughness surfaces (which model the reflective/transparentproperties of such roughness in the presence of small sub-wavelengthroughness elements), and/or the like; ande) Re-evaluating the efficiency of LED by varying optimizationparameters describing roughness where the variation of any one parameterin the set of parameters can be either random, or continuous (whereincontinuous variation includes also no variation). The parametervariation can be performed, for example, according to a geneticalgorithm where models with sets of improved parameters are allowed to“cross-breed”, wherein “cross-breeding” includes overlapping a parameterspace of one model with a parameter space of another model in variouscombinations to create one or more new sets of optimization parametersfor evaluation. Furthermore, the “cross-breeding” can includeintroducing randomness into one or more parameters of the new sets ofoptimization parameters.

While shown and described herein as a method of designing and/orfabricating an emitting device to improve extraction of light from thedevice, it is understood that aspects of the invention further providevarious alternative embodiments. For example, aspects of the inventioncan be implemented to facilitate the transmission of light within thedevice, e.g., as part of optical pumping of a laser light generatingstructure, excitation of a carrier gas using a laser pulse, and/or thelike. Similarly, an embodiment of the invention can be implemented inconjunction with a sensing device, such as a photosensor or aphotodetector. In each case, a profiled surface can be included in anexterior surface of the device and/or an interface of two adjacentlayers of the device in order to facilitate the transmission of lightthrough the interface in a desired direction.

In one embodiment, the invention provides a method of designing and/orfabricating a circuit that includes one or more of the devices designedand fabricated as described herein. To this extent, FIG. 10 shows anillustrative flow diagram for fabricating a circuit 126 according to anembodiment. Initially, a user can utilize a device design system 110 togenerate a device design 112 for a semiconductor device as describedherein. The device design 112 can comprise program code, which can beused by a device fabrication system 114 to generate a set of physicaldevices 116 according to the features defined by the device design 112.Similarly, the device design 112 can be provided to a circuit designsystem 120 (e.g., as an available component for use in circuits), whicha user can utilize to generate a circuit design 122 (e.g., by connectingone or more inputs and outputs to various devices included in acircuit). The circuit design 122 can comprise program code that includesa device designed as described herein. In any event, the circuit design122 and/or one or more physical devices 116 can be provided to a circuitfabrication system 124, which can generate a physical circuit 126according to the circuit design 122. The physical circuit 126 caninclude one or more devices 116 designed as described herein.

In another embodiment, the invention provides a device design system 110for designing and/or a device fabrication system 114 for fabricating asemiconductor device 116 as described herein. In this case, the system110, 114 can comprise a general purpose computing device, which isprogrammed to implement a method of designing and/or fabricating thesemiconductor device 116 as described herein. Similarly, an embodimentof the invention provides a circuit design system 120 for designingand/or a circuit fabrication system 124 for fabricating a circuit 126that includes at least one device 116 designed and/or fabricated asdescribed herein. In this case, the system 120, 124 can comprise ageneral purpose computing device, which is programmed to implement amethod of designing and/or fabricating the circuit 126 including atleast one semiconductor device 116 as described herein.

In still another embodiment, the invention provides a computer programfixed in at least one computer-readable medium, which when executed,enables a computer system to implement a method of designing and/orfabricating a semiconductor device as described herein. For example, thecomputer program can enable the device design system 110 to generate thedevice design 112 as described herein. To this extent, thecomputer-readable medium includes program code, which implements some orall of a process described herein when executed by the computer system.It is understood that the term “computer-readable medium” comprises oneor more of any type of tangible medium of expression, now known or laterdeveloped, from which a stored copy of the program code can beperceived, reproduced, or otherwise communicated by a computing device.

In another embodiment, the invention provides a method of providing acopy of program code, which implements some or all of a processdescribed herein when executed by a computer system. In this case, acomputer system can process a copy of the program code to generate andtransmit, for reception at a second, distinct location, a set of datasignals that has one or more of its characteristics set and/or changedin such a manner as to encode a copy of the program code in the set ofdata signals. Similarly, an embodiment of the invention provides amethod of acquiring a copy of program code that implements some or allof a process described herein, which includes a computer systemreceiving the set of data signals described herein, and translating theset of data signals into a copy of the computer program fixed in atleast one computer-readable medium. In either case, the set of datasignals can be transmitted/received using any type of communicationslink.

In still another embodiment, the invention provides a method ofgenerating a device design system 110 for designing and/or a devicefabrication system 114 for fabricating a semiconductor device asdescribed herein. In this case, a computer system can be obtained (e.g.,created, maintained, made available, etc.) and one or more componentsfor performing a process described herein can be obtained (e.g.,created, purchased, used, modified, etc.) and deployed to the computersystem. To this extent, the deployment can comprise one or more of: (1)installing program code on a computing device; (2) adding one or morecomputing and/or I/O devices to the computer system; (3) incorporatingand/or modifying the computer system to enable it to perform a processdescribed herein; and/or the like.

The foregoing description of various aspects of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and obviously, many modifications and variations arepossible. Such modifications and variations that may be apparent to anindividual in the art are included within the scope of the invention asdefined by the accompanying claims.

What is claimed is:
 1. A device comprising: an at least partiallytransparent layer having a first side and a second side, whereinradiation enters the at least partially transparent layer through thefirst side and exits the at least partially transparent layer throughthe second side, and wherein at least one of the first side or thesecond side comprises a profiled surface, the profiled surfaceincluding: a set of large roughness components providing a firstvariation of the profiled surface having a characteristic scaleapproximately an order of magnitude larger than a target wavelength ofthe radiation, wherein the set of large roughness components comprise aseries of truncated shapes, wherein a first portion of the series oftruncated shapes is inversely truncated and a second portion of theseries of truncated shapes is not inversely truncated; and a set ofsmall roughness components providing a second variation of the profiledsurface having a characteristic scale on the order of the targetwavelength of the radiation, wherein the set of small roughnesscomponents are superimposed on the set of large roughness components,and wherein the characteristic scale for the set of large roughnesscomponents and the characteristic scale for the set of small roughnesscomponents are selected to increase a transmission of radiation exitingthe at least partially transparent layer by at least 5% as compared to acomparable at least partially transparent layer having a surface withoutthe set of small roughness components.
 2. The device of claim 1, whereinthe partially transparent layer comprises sapphire.
 3. The device ofclaim 1, wherein each of the first portion and the second portionoccupies at least twenty percent of a lateral area of the profiledsurface.
 4. The device of claim 1, wherein the target wavelength of theradiation is between 250 nanometers and 350 nanometers.
 5. The device ofclaim 1, wherein the characteristic scale for the set of large roughnesscomponents and the characteristic scale for the set of small roughnesscomponents are selected to provide a transmission of at least 93% forthe radiation exiting the at least partially transparent layer.
 6. Thedevice of claim 1, wherein the set of large roughness components furthercomprises a series of non-truncated shapes interspersed with the seriesof truncated shapes.
 7. The device of claim 6, wherein each of theseries of non-truncated shapes and the series of truncated shapesoccupies at least twenty percent of a lateral area of the profiledsurface.
 8. The device of claim 1, wherein the set of small roughnesscomponents are oriented normal to a surface of the set of largeroughness components.
 9. A method comprising: designing a profiledsurface for an at least partially transparent layer of a device, whereinradiation passes through the profiled surface during operation of thedevice, wherein the profiled surface includes: a set of large roughnesscomponents providing a first non-uniform variation of the profiledsurface having a characteristic scale approximately an order ofmagnitude larger than a target wavelength of the radiation, wherein theset of large roughness components comprise a series of truncated shapes,wherein a first portion of the series of truncated shapes is inverselytruncated and a second portion of the series of truncated shapes is notinversely truncated; and a set of small roughness components providing asecond non-uniform variation of the profiled surface having acharacteristic scale on the order of the target wavelength of theradiation, wherein the set of small roughness components aresuperimposed on the set of large roughness components, and wherein thecharacteristic scale for the set of large roughness components and thecharacteristic scale for the set of small roughness components areselected to increase a transmission of radiation exiting the at leastpartially transparent layer by at least 5% as compared to a comparableat least partially transparent layer having a surface without the set ofsmall roughness components.
 10. The method of claim 9, furthercomprising fabricating the device including the at least partiallytransparent layer, wherein the fabricating includes fabricating theprofiled surface.
 11. The method of claim 10, wherein the fabricatingthe profiled surface includes forming at least one of: the set of largeroughness components or the set of small roughness components using atleast one of: selective deposition or selective etching of nanodots. 12.The method of claim 10, wherein fabricating the profiled surfaceincludes performing a simulation using ray tracing and a geneticalgorithm.
 13. An emitting device comprising: an active regionconfigured to generate radiation having a peak wavelength; and an atleast partially transparent layer on a first side of the active region,wherein radiation generated in the active region passes through the atleast partially transparent layer, and wherein the at least partiallytransparent layer includes at least one profiled surface, wherein the atleast one profiled surface includes: a set of large roughness componentsproviding a first variation of the profiled surface having acharacteristic scale approximately an order of magnitude larger than atarget wavelength of the radiation, wherein the set of large roughnesscomponents comprise a series of truncated shapes, wherein a firstportion of the series of truncated shapes is inversely truncated and asecond portion of the series of truncated shapes is not inverselytruncated; and a set of small roughness components providing a secondvariation of the profiled surface having a characteristic scale on theorder of the target wavelength of the radiation, wherein the set ofsmall roughness components are superimposed on the set of largeroughness components, and wherein the characteristic scale for the setof large roughness components and the characteristic scale for the setof small roughness components are selected to increase a transmission ofradiation exiting the at least partially transparent layer by at least5% as compared to a comparable at least partially transparent layerhaving a surface without the set of small roughness components.
 14. Thedevice of claim 13, wherein the partially transparent layer comprisessapphire.
 15. The device of claim 13, wherein the set of small roughnesscomponents form a photonic crystal.
 16. The device of claim 13, whereineach of the first portion and the second portion occupies at leasttwenty percent of a lateral area of the profiled surface.
 17. The deviceof claim 13, wherein the set of large roughness components furthercomprises a series of non-truncated shapes interspersed with the seriesof truncated shapes.
 18. The device of claim 17, wherein each of theseries of non-truncated shapes and the series of truncated shapesoccupies at least twenty percent of a lateral area of the profiledsurface.
 19. The device of claim 13, wherein the characteristic scalefor the set of large roughness components and the characteristic scalefor the set of small roughness components are selected to provide atransmission of at least 93% for the radiation exiting the at leastpartially transparent layer.
 20. The device of claim 13, wherein the setof small roughness components are oriented normal to a surface of theset of large roughness components.